One prior art game ball comprises a spherical core member formed of flexible and resilient molded polyurethane foam and a cover portion comprising a leather member stitched over and enclosing the core member. The leather cover may be stitched over the core of polyurethane foam by embedding yarn windings or adhesive between the core and the cover. Since the outer surface of the urethane core is not corrugated, after repeated pitching and catching actions as a result of playing games, the core may loosen from the cover. In such a manner, the pitching moment or accuracy of the ball will be seriously affected.
Another prior art game ball discloses a composite ball having a spherical core and a cover, wherein said core is formed from isocyanate and a mixture of catalyst and blowing agent. However, such an isocyanate material will increase the production cost of ball as compared to conventional balls, such as balls made of cork and rubber core, or PVC foamed balls.
Another prior art baseball includes an improvement wherein the core consists essentially of a single spherical mass of blown ethylene vinyl acetate copolymer thermoplastic resin having 12% to 30% by weight polymerized vinyl acetate units. Such a ball, however, is still more expensive than conventional baseballs.
Another prior art publication discloses a centerless thick-walled game ball comprising a hollow spherical mass, a cork-rubber capsule, thread windings and a cover exhibits a greater moment of inertia compared to filled balls so as to improve aerodynamic characteristics of the ball. Since such a ball should be made of equal weight and size as a conventional ball, the density of the cork-rubber capsule must be increased to compensate the hollow core whereby a heavier filler should be incorporated into the rubber capsule composite which will be easily broken in use. Thus, a special high-density rubber should be provided which necessarily increases the cost of ball production.
The conventional arts do not disclose the corrugate or rough surface on the core cover to increase the binding friction between the core and the outermost cover so that, according to conventional balls, the outermost cover thereof may be loosened from the core after being used over a period of time.
The present inventors have found these defects of conventional balls. The improvements over the prior balls have been made by the present inventors in view of the following specification and the accompanying drawings.